ok so ive had an HP desktop for about a year now and i was looking to upgrade it so that i would be able to run Empire Total War.
here are the specs(stock)
AMD Phenom X4 9650 Quadcore Processor
NVIDIA GeForce 6150 SE graphics
Vista
7 gig RAM

I think the only thing that needs upgrading is the graphics card hopefully im not trying to go all out and spend crazy money i just want it to run the game without skipping and lag like what it had done with medieval total war 2.

However, it would be nice to know how much your power supply can put out. If it's too small, neither of those are going to work unless you upgrade. Your current one may be ok though. What is your computer's model?

edit: Vinman has the right idea...that ati card is great. The nvidia one has the same specs as lhuser's, but is cheaper...about right for that card. You can still get better for the price. That PSU is ok as well.